Engines convert energy into work. In that sense, they power the devices we use every day: automobiles, airplanes, refrigerators. But in a larger sense, engines drive the world's economy. For all the efficiencies afforded by the Internet revolution, people and things still make their way around the world under the power of engines.
Most automobile engines convert fuel into energy using an internal combustion engine powered by gasoline, propane, or diesel fuel. Because of the enormous amount of fuel converted into energy by internal combustion engines, even a small improvement in fuel efficiency provides a significant overall fuel savings.
Improved fuel efficiency can also provide substantial environmental benefits. Since less fuel is being converted into energy, a proportionately smaller amount of harmful emissions are being produced. Again, because of the sheer number of internal combustion engines in use, this can create a significant overall improvement. Further benefits may be obtained if the process of converting fuel into energy itself produces cleaner exhaust.
In a conventional internal combustion engine, gasoline and air combust to provide energy that may be used (for example) to run an automobile. FIGS. 1A to 1D show a typical cycle for an internal combustion engine. In FIG. 1A, gas and air are introduced through an inlet 115 into a cylinder 110 including a piston 120. In FIG. 1B, piston 120 is compressed. In FIG. 1C, a spark is introduced into cylinder 110 via a spark plug 130, and the air and gasoline combust. The force of combustion drives a piston downward, providing energy that may be used to drive a load (e.g., to turn a crank shaft of an automobile). In FIG. 1D, the product of the combustion is exhausted. The exhaust of a conventional internal combustion engine generally includes not only carbon dioxide and water, but also harmful substances such as carbon monoxide and nitrous oxide.